Sprite (computer graphics)
Sprite is a computer graphics term for a two-dimensional bitmap that is integrated into a larger scene, most often in a 2D video game. Originally sprites referred to independent objects that are composited together, by hardware, with other elements such as a background. The composition occurs as each scan line is prepared for the video output device, such as a CRT, without involvement of the main CPU and without the need for a full-screen frame buffer. Sprites can be positioned or altered by setting attributes used during the hardware composition process. Examples of systems with hardware sprites include the Atari 8-bit family, Commodore 64, Amiga, Nintendo Entertainment System, Sega Genesis, and many coin-operated arcade machines of the 1980s. Sprite hardware varies in how many sprites are supported, how many can be displayed on a single scan line (which is often a lower number), the dimensions and colors of each sprite, and special effects such as scaling or reporting pixel-precise overlap. Use of the term sprite has expanded to refer to any two-dimensional bitmap used as part of a graphics display, even if drawn into a frame buffer (by either software or a GPU) instead of being composited on-the-fly at display time. The act of manually creating sprites, as opposed to pre-rendering them or using digitized images, is a form of pixel art. It is sometimes referred to as spriting, especially in the hobbyist community. History The use of sprites originated with arcade games. The first video game to represent player characters as human player images was Taito's Basketball, which was licensed in February 1974 to Midway, releasing it as TV Basketball in North America.Video Game Firsts, The Golden Age Arcade Historian (November 22, 2013)[http://flyers.arcade-museum.com/?page=wide-flyer&db=videodb&id=4036&image=2 Basketball Flyer] (1974), Arcade Flyer Museum Signetics devised the first chips capable of generating sprite graphics (referred to as objects by Signetics) for home systems. The Signetics 2636 video processors were first used in the 1978 1292 Advanced Programmable Video System and later in the 1979 Elektor TV Games Computer. The Atari VCS, released in 1977, features a hardware sprite implementation where five graphical objects can be moved independently of the game playfield. The term sprite was not in use at the time. The VCS's sprites are called movable objects in the programming manual, further identified as two players, two missiles, and one ball. These each consist of a single row of pixels that are displayed on a scan line. To produce a two-dimensional shape, the sprite's single-row bitmap is altered by software from one scan line to the next. The 1979 Atari 400 and 800 home computers feature similar, but more elaborate, circuitry capable of moving eight single-color objects per scan line: four 8-bit wide players and four 2-bit wide missiles. Each is the full height of the display—a long, thin strip. DMA from a table in memory automatically sets the graphics pattern registers for each scan line. Hardware registers control the horizontal position of each player and missile. Vertical motion is achieved by moving the bitmap data within a player or missile's strip. The feature was called player/missile graphics by Atari. The Namco Galaxian arcade system board, for the 1979 arcade game Galaxian, featured animated, multi-colored sprites. It pioneered a sprite system that animated pre-loaded sprites over a scrolling background, which became the basis for Nintendo's Radar Scope and Donkey Kong arcade hardware and home consoles such as the Nintendo Entertainment System.Making the Famicom a Reality, Nikkei Electronics (September 12, 1994) According to Steve Golson from General Computer Corporation, the term "stamp" was used instead of "sprite" at the time. The term sprite was first used in the graphic sense by one of the definers of the Texas Instruments 9918(A) video display processor (VDP). The term was derived from the fact that sprites, rather than being part of the bitmap data in the framebuffer, instead "floated" around on top without affecting the data in the framebuffer below, much like a ghost or "sprite". By this time, sprites had advanced to the point where complete two-dimensional shapes could be moved around the screen horizontally and vertically with minimal software overhead. Systems with hardware sprites These are base hardware specs and do not include additional programming techniques, such as using raster interrupts to repurpose sprites mid-frame. Use in 3D rendering 2D images with alpha channels constrained to face the camera may be used in 3D graphics. They are common for rendering vegetation, to approximate distant objects, or for particle effects. These are sometimes called "billboards" or "Z-sprites". If rendered on the fly to cache an approximate view of an underlying 3D model, such sprites are called impostors. Modern GPU hardware can mimic sprites with two texture-mapped triangles or specific primitives such as point sprites. Synonyms Some hardware makers used terms other than sprite. Player/Missile Graphics was a term used by Atari, Inc. for hardware-generated sprites in the company's early coin-op games, the Atari 2600 and 5200 consoles, and the Atari 8-bit computers. The term reflected the usage for both characters ("players") and smaller associated objects ("missiles") that share the same color. Movable Object Block, or MOB, was used in MOS Technology's graphics chip literature (data sheets, etc.) However, Commodore, the main user of MOS chips and the owner of MOS for most of the chip maker's lifetime, used the term sprite for the Commodore 64. The developer manuals for the Nintendo Entertainment System, Super NES, and Game Boy refer to sprites as OBJ'''s (short for "objects"), and the region of RAM used to store sprite attributes and coordinates was known as '''OAM (Object Attribute Memory). This also applies on the Game Boy Advance and Nintendo DS handheld systems. See also * 2.5D * Layers (digital image editing) References Category:Computer graphics Category:Video game design Category:Video game development